With the development of display technology, the flat panel device, such as Liquid Crystal Display (LCD) possesses advantages of high image quality, power saving, thin body and wide application scope. Thus, it has been widely applied in various consumer electrical products, such as mobile phone, television, personal digital assistant, digital camera, notebook, laptop, and becomes the major display device.
Most of the liquid crystal displays on the present market are back light type liquid crystal displays, which comprise a liquid crystal display panel and a back light module. The working principle of the liquid crystal display panel is to locate liquid crystal molecules between two parallel glass substrates, and a plurality of vertical and horizontal tiny electrical wires are between the two glass substrates. The light of back light module is reflected to generate images by applying driving voltages to control whether the liquid crystal molecules to be changed directions.
Generally, the liquid crystal display panel comprises a CF (Color Filter) substrate, a TFT (Thin Film Transistor) array substrate, LC (Liquid Crystal) sandwiched between the CF substrate and TFT substrate and sealant. The formation process generally comprises: a forepart Array process (thin film, photo, etching and stripping), a middle Cell process (Lamination of the TFT substrate and the CF substrate) and a post module assembly process (Attachment of the driving IC and the printed circuit board). The forepart Array process is mainly to form the TFT substrate for controlling the movement of the liquid crystal molecules; the middle Cell process is mainly to add liquid crystal between the TFT substrate and the CF substrate; the post module assembly process is mainly the driving IC attachment and the integration of the printed circuit board. Thus, the liquid crystal molecules are driven to rotate and display pictures.
In the traditional liquid crystal display panel, At one side of the color filter, a layer of BM (Black Matrix) is manufactured which is employed to divide adjacent color resists to shield the gaps of the color resists and to prevent the light leakage or the color mix; the skill of manufacturing the black matrix on the TFT array substrate is called BOA (BM On Array, the Black Matrix is adhered on the array substrate). BOA can solve the problems that the shielding areas do not match due to the upper, lower substrates misalignment, which particularly useful to the curved display. COA (Color filter On Array) technology is a skill to manufacture the RGB color resists which are previously manufactured on the color filter on the TFT array substrate. The COA technology can improve the signal delay on the metal line to raise the panel aperture ratio and improve the display quality of the panel.
FIG. 1 is a diagram of a color filter after a black matrix is manufactured. As shown in FIG. 1, the black matrix 200 is a first manufacture process of the color filter 100. Therefore, referring the alignment mark of the previous process is not necessary for the manufacture process of the black matrix. In the liquid crystal display panel of BOA structure, the black matrix is manufactured at onside of the array substrate. Before manufacturing the black matrix, the processes of other patterns have already been accomplished. Thus, referring the alignment mark of the previous process is not necessary as manufacturing the black matrix. However, the black matrix has higher OD (optical density). Thus, it will cause interference to the recognition to the mask alignment mark after the coating, and might result in the unable alignment of the stepper. If the black matrix material having lower optical density is used, the recognition ability of the alignment mark after coating can be improved but the shielding result of the black matrix can be seriously influenced.
FIG. 2 is a diagram of a TFT array substrate coated a black matrix color resist system. FIG. 3 is a sectional diagram of a circle area in FIG. 2. As shown in FIG. 2, FIG. 3, after the TFT array substrate 300 is coated with the black matrix thin film 400, the black matrix thin film 400 completely covers the alignment mask 500. Because the typical value of the thickness of the black matrix thin film 400 is 1 μm, and after it covers the alignment mask 500, the level difference d1 of the position of the alignment mask 500 and the adjacent area is reduced. Therefore, even utilizing the method of contour recognition is very difficult to recognize the accurate position of the alignment mask 500.